There's no playbook you can run to make a social app go viral.
Social media is neither. Ben Thompson's aggregator aside from the B2C/B dichotomy shines in this example. Snap and Twitter notoriously struggled with ad sales, for example.
That isn't notoriously struggling. The statement that the ad component is relatively easy is borne out by the facts. There are zero companies doing lots of ad revenue with very few users, and practically every service with hundreds of millions to billions of users spending their time looking at some service is doing significant ad revenue.
The only way one can think they struggled is if compared to the two wildly outlying, greatest ad revenue machines in the history of the world.
B2C people expect perfection for free and will balk at the slightest complication.
Don't underestimate luck, it causes you to overestimate your own abilities. Thousands of other startups with seemingly great ideas, equally smart founders and equally "sound" business plans all failed. Some of the survivors of these competitions will have won due to their savvy, but plenty will have won from sheer dumb luck (survivorship bias).
Yet, this team is one of the few that have succeeded at all of these challenges before.
I'm excited to watch how they build this business. Success is uncertain, but observing their actions will be a case study in growth tactics.